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    <title>Title</title>
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<h1>第三章 基本概念</h1>
<button onclick="typeofTest()">typeof测试</button>
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<button onclick="undefinedTest()">undefined测试</button>
<button onclick="infinityTest()">无穷测试</button>
<button onclick="objectTest()">对象测试</button>
<script type="text/javascript" src="../js/ch03.js"></script>
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